Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Correctly update atomics in IoDriverMetrics #4725

Merged
merged 1 commit into from
May 30, 2022
Merged

Conversation

asomers
Copy link
Contributor

@asomers asomers commented May 30, 2022

Updating an atomic variable with a load followed by a store is racy. It
defeats the entire purpose of using atomic variables, and can result in
"lost" updates. Instead, use fetch_add .

Motivation

Avoid inaccurate metrics due to update races.

Solution

Always use atomic instructions to update atomic variables.

@github-actions github-actions bot added the R-loom Run loom tests on this PR label May 30, 2022
Updating an atomic variable with a load followed by a store is racy.  It
defeats the entire purpose of using atomic variables, and can result in
"lost" updates.  Instead, use fetch_add .
@asomers
Copy link
Contributor Author

asomers commented May 30, 2022

I think the failure on windows-latest is spurious. The --unstable test on windows-latest worked, after all.

@Darksonn Darksonn added A-tokio Area: The main tokio crate M-metrics Module: tokio/runtime/metrics labels May 30, 2022
Copy link
Contributor

@Darksonn Darksonn left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Thanks. I'm surprised this wasn't caught in the PR originally adding this.

@Darksonn Darksonn merged commit 6c0a994 into tokio-rs:master May 30, 2022
@asomers asomers deleted the atomic branch May 30, 2022 14:12
@vitalyd
Copy link
Contributor

vitalyd commented May 31, 2022

(just lurking) The original code might've been intentional since fetch_add(1, Relaxed) is going to issue a lock'd instruction on x86/64 (godbolt). An argument could be made (I wouldn't make it without some benchmarks to support this, but ...) that for stats/metrics, the chance of a lost update is the price to pay to generate lighter weight code (i.e. the original code is a normal store, no memory fences).

@Darksonn
Copy link
Contributor

Darksonn commented Jun 3, 2022

@vitalyd The original argument for doing it appears to be that only the IO driver changes these counts, so there isn't actually any race. However, looking at the code it does not seem like that is the case. The incr_fd_count method can be called in parallel for example.

crapStone pushed a commit to Calciumdibromid/CaBr2 that referenced this pull request Jun 11, 2022
This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [tokio](https://tokio.rs) ([source](https://github.com/tokio-rs/tokio)) | dependencies | minor | `1.18.2` -> `1.19.1` |
| [tokio](https://tokio.rs) ([source](https://github.com/tokio-rs/tokio)) | dev-dependencies | minor | `1.18.2` -> `1.19.1` |

---

### Release Notes

<details>
<summary>tokio-rs/tokio</summary>

### [`v1.19.1`](https://github.com/tokio-rs/tokio/releases/tag/tokio-1.19.1)

[Compare Source](tokio-rs/tokio@tokio-1.19.0...tokio-1.19.1)

##### 1.19.1 (June 5, 2022)

This release fixes a bug in `Notified::enable`. ([#&#8203;4747])

[#&#8203;4747]: tokio-rs/tokio#4747

### [`v1.19.0`](https://github.com/tokio-rs/tokio/releases/tag/tokio-1.19.0)

[Compare Source](tokio-rs/tokio@tokio-1.18.2...tokio-1.19.0)

##### 1.19.0 (June 3, 2022)

##### Added

-   runtime: add `is_finished` method for `JoinHandle` and `AbortHandle` ([#&#8203;4709])
-   runtime: make global queue and event polling intervals configurable ([#&#8203;4671])
-   sync: add `Notified::enable` ([#&#8203;4705])
-   sync: add `watch::Sender::send_if_modified` ([#&#8203;4591])
-   sync: add resubscribe method to broadcast::Receiver ([#&#8203;4607])
-   net: add `take_error` to `TcpSocket` and `TcpStream` ([#&#8203;4739])

##### Changed

-   io: refactor out usage of Weak in the io handle ([#&#8203;4656])

##### Fixed

-   macros: avoid starvation in `join!` and `try_join!` ([#&#8203;4624])

##### Documented

-   runtime: clarify semantics of tasks outliving `block_on` ([#&#8203;4729])
-   time: fix example for `MissedTickBehavior::Burst` ([#&#8203;4713])

##### Unstable

-   metrics: correctly update atomics in `IoDriverMetrics` ([#&#8203;4725])
-   metrics: fix compilation with unstable, process, and rt, but without net ([#&#8203;4682])
-   task: add `#[track_caller]` to `JoinSet`/`JoinMap` ([#&#8203;4697])
-   task: add `Builder::{spawn_on, spawn_local_on, spawn_blocking_on}` ([#&#8203;4683])
-   task: add `consume_budget` for cooperative scheduling ([#&#8203;4498])
-   task: add `join_set::Builder` for configuring `JoinSet` tasks ([#&#8203;4687])
-   task: update return value of `JoinSet::join_one` ([#&#8203;4726])

[#&#8203;4498]: tokio-rs/tokio#4498

[#&#8203;4591]: tokio-rs/tokio#4591

[#&#8203;4607]: tokio-rs/tokio#4607

[#&#8203;4624]: tokio-rs/tokio#4624

[#&#8203;4656]: tokio-rs/tokio#4656

[#&#8203;4671]: tokio-rs/tokio#4671

[#&#8203;4682]: tokio-rs/tokio#4682

[#&#8203;4683]: tokio-rs/tokio#4683

[#&#8203;4687]: tokio-rs/tokio#4687

[#&#8203;4697]: tokio-rs/tokio#4697

[#&#8203;4705]: tokio-rs/tokio#4705

[#&#8203;4709]: tokio-rs/tokio#4709

[#&#8203;4713]: tokio-rs/tokio#4713

[#&#8203;4725]: tokio-rs/tokio#4725

[#&#8203;4726]: tokio-rs/tokio#4726

[#&#8203;4729]: tokio-rs/tokio#4729

[#&#8203;4739]: tokio-rs/tokio#4739

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about these updates again.

---

 - [x] <!-- rebase-check -->If you want to rebase/retry this PR, click this checkbox.

---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).

Co-authored-by: cabr2-bot <cabr2.help@gmail.com>
Reviewed-on: https://codeberg.org/Calciumdibromid/CaBr2/pulls/1394
Reviewed-by: crapStone <crapstone@noreply.codeberg.org>
Co-authored-by: Calciumdibromid Bot <cabr2_bot@noreply.codeberg.org>
Co-committed-by: Calciumdibromid Bot <cabr2_bot@noreply.codeberg.org>
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Labels
A-tokio Area: The main tokio crate M-metrics Module: tokio/runtime/metrics R-loom Run loom tests on this PR
Projects
None yet
Development

Successfully merging this pull request may close these issues.

3 participants